docs(build): migrate from Makefile to justfile

why: All other projects in the ecosystem use justfiles for docs builds.
The Makefile was the last holdout, creating inconsistency across repos.
what:
- Replace docs/Makefile with docs/justfile (same recipes, just syntax)
- Uses dirhtml builder for clean URLs (matches ecosystem standard)
- Update CI workflow to use `just html` instead of `make html`
- Update root Makefile doc targets to delegate to justfile
- Port 8034 preserved from original Makefile

Author: tony

.github/workflows/docs.yml

@@ -72,7 +72,7 @@ jobs:
       - name: Build documentation
         if: env.PUBLISH == 'true'
         run: |
-          pushd docs; make SPHINXBUILD='uv run sphinx-build' html; popd
+          cd docs && just html
 
       - name: Configure AWS Credentials
         if: env.PUBLISH == 'true'

Makefile

@@ -21,13 +21,13 @@ watch_test:
 	if command -v entr > /dev/null; then ${PY_FILES} | entr -c $(MAKE) test; else $(MAKE) test entr_warn; fi
 
 build_docs:
-	$(MAKE) -C docs html
+	just -f docs/justfile html
 
 start_docs:
-	$(MAKE) -C docs start
+	just -f docs/justfile start
 
 design_docs:
-	$(MAKE) -C docs design
+	just -f docs/justfile design
 
 ruff_format:
 	uv run ruff format .